Goal Seek in Excel
Excel marked cell which the result is set as a result of the planned analysis. In this example this is a value of $1,000,000. In the Value field, enter the planned value of 1000000. As By changing cell field you should choose cell with count of pieces. In this example it is C3 cell.
After clicking OK new dialog box appears. It is status of Goal Seek. Excel asks you if everything is ok. If not click Cancel and nothing will change in your table. In this example the result is correct so click OK.
The result is 4 347 pieces. That how many pieces you can afford.
As you see Goal Seek is very easy way to calculate results. Try to learn for your own with more difficult examples.